1. Field
The present disclosure relates to positive active materials, secondary batteries including the positive active materials, and methods of manufacturing the secondary batteries, and more particularly, to positive active materials having improved initial efficiency, capacity, and lifespan characteristics, secondary batteries including the positive active materials, and methods of manufacturing the positive active materials.
2. Description of the Related Art
With the reduced weight and increased functionality of mobile electronic devices such as laptop computers, video cameras, and mobile phones, batteries used as a driving energy source of such devices are also increased in terms of capacity and energy density. Therefore, there is an increasing need for secondary batteries that may be reversibly charged and discharged and used multiple times.
Among secondary batteries, lithium ion batteries (LiB) and/or sodium ion batteries using sodium ions have been used as power sources for many mobile devices due to their high energy densities and ease of design. Recently, LiBs and/or sodium ion batteries have been used as power supplies for electric vehicles and power storage in addition to mobile IT devices, and thus, research has been expanded to LiB materials appropriate for manufacturing LiBs and/or sodium ion batteries with high energy density and long lifespan.
Regarding the LiB materials, when a method of coating a positive electrode surface by using a coating material is used, the battery performance may be improved to a satisfactory level since a positive active material is easily modified while using a conventional positive active material.
An electrochemically stable oxide or phosphate is widely used as a coating material in such a coating method. The coating material blocks a direct contact between the positive electrode surface and an electrolyte to inhibit leakage of ions due to the contact with the electrolyte, dissolution of oxygen ions of a positive electrode oxide, or the like in order to improve the structural stability and thermal stability of the positive active material.
However, the method of coating the positive electrode surface by using the coating material such as the electrochemically stable oxide or phosphate may decrease the specific capacity and active reaction surface area of the LiB due to the addition of the coating material that does not directly participate in a charge and discharge reaction, which may cause an increase in the interface resistance between the positive active material and the coating material and a decrease in the high rate charge and discharge characteristics.
Also, due to recent increased demand for high energy density batteries, research on high voltage positive active materials has been actively performed. Accordingly, research on coating materials that inhibit the oxidation of an electrolyte on a high voltage positive active material surface is further needed.
Accordingly, there is still a demand for a positive active material having improved initial efficiency, capacity, and lifespan characteristics at a high voltage, a secondary battery including the positive active material, and a method of manufacturing the positive active material.